1. Field of the Invention
The present invention relates to a production apparatus of expansion-molded articles, and particularly to a production apparatus of expansion-molded articles, which has been designed to effectively enhance the ability to fill foamed particles into a mold. The present invention also relates to an auxiliary member for transfer of foamed particles used in the production apparatus of expansion-molded articles. The present invention is further concerned with a method for producing an expansion-molded article using this apparatus.
2. Description of the Background Art
As methods of transferring foamed particles stored in a hopper to a mold and filling them into the mold upon molding of the foamed particles in the mold, there have heretofore been known the following methods:
(1) a method in which a mold is evacuated upon filling to set up an air current, and foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open No. 3762/1988); PA1 (2) a method in which compressed air is ejected from a compressed-air ejection nozzle of a foamed article feeder installed on a mold to set up an air current, and foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open Nos. 43762/1988, 46623/1987 and 77331/1993); and PA1 (3) a method in which foamed particles within a hopper are kept under pressure to set up an air current by using the pressure within the hopper and the method (2) in combination, and the foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open Nos. 176747/1985, 79625/1986 and 87327/1987, and Japanese Patent Publication No. 87364/1993).
However, only a differential pressure of 1 atm can be obtained at the most by the method (1). Therefore, the foamed particles have been unable to be filled at a high filling density into the mold. The method (1) has hence involved a problem that the resulting expansion-molded article tends to have poor interparticle fusion bonding or high shrinkage factor, and so percent defective increases. In addition, according to this method, it has also been difficult to conduct blow back of excess foamed particles not filled into the mold into the hopper.
If the blow back of the foamed particles is only incompletely carried out, there is a possibility that the foamed particles may remain in a space defined in the rear of a piston for closing a foamed particle introducing opening in the mold while the piston is being moved forward, and so the backward movement of the piston may be blocked by the foamed particles remained in the space defined in the rear of the piston, resulting in a failure to fully fill new foamed particles into the mold upon the next molding.
The method (2) permits the filling of the foamed particles at a higher filling density than the method (1). However, the method (2) has involved a problem that if the form of a mold cavity becomes somewhat complicated, a failure in filling of the foamed particles occurs, and consequently many of the resulting expansion-molded articles tend to have poor interparticle fusion bonding or high shrinkage factor, and so percent defective increases.
The failure in filling of the foamed particles caused by the complicated cavity form may be improved to some extent by installing an additional feeder in the mold. In order to install the additional feeder, however, it is necessary to newly make an additional hole for installing the feeder in the mold. However, the installation of the additional feeder involves undesirable problems that the strength of the mold may possibly be markedly deteriorated according to the position of the hole for installing the new feeder, and the installation of more feeders increases the number of marks of the tip form of the feeder transferred to the surface of the resulting expansion-molded article to deteriorate the external appearance of the expansion-molded article. In some cases, it has been impossible in itself to install the additional feeder. Namely, the position where the feeder is intended to install is a position corresponding to the surface of the resulting molded article on which the transferred mark should not be left, or in some cases the additional feeder may not be installed due to the presence of piping and the like in the machine. After all, the installation of the additional feeder cannot be a preferable means for solution.
The method (3) has involved a problem that since the foamed particles kept under pressure in the hopper are exposed to a pressure lower than the pressure within the hopper upon their filling, the foamed particles undergo volume expansion within the hopper, at the outlet of the hopper, or within a pipe, and the expanded foamed particles tend to clog the outlet or the pipe and the like. The clogging of the outlet or the pipe and the like with the foamed particles has offered a problem that a failure in filling of the foamed particles into the mold occurs. There has also been involved a problem that since the interior of the hopper is pressurized, blow back of excess foamed particles into the hopper cannot be effectively carried out.